Orthopedic alignment currently involves cycles of trial and error. For example, leg alignment requires a technique that approximates alignment in which the surgeon makes one of the distal femoral cut and the proximal tibial cut based on experience, mechanical jigs, and visual alignment. Typically, the proximal tibial cut is made so as to remove the least amount of the proximal tibia, while ensuring sufficient removal of diseased or otherwise undesirable bone. The remaining femoral cuts are made to complete shaping of the femur to receive a femoral prosthesis. After the femoral and tibial cuts are complete, the femoral prosthesis and the tibial prosthesis, or trial versions thereof, are temporarily implanted and the surgeon reviews leg alignment. Typically, no adjustments are made if the leg is within a few degrees varus or valgus of the mechanical axis. An insert has a bearing surface that allows articulation of the leg. A set of shims can be coupled to the insert. The shims are used to change the thickness of the insert. A shim and insert combination is chosen that produces the best subjective movement characteristics of the joint through a full the range of motion. The surgeon may modify the bone or perform soft tissue tensioning to affect load, rotation or alignment characteristics. In general, the implant procedure is performed using the subjective skills of the surgeon to achieve appropriate leg alignment, rotation, balance, and soft tissue tension-loading.
Even with mechanical jigs, trialing, and advanced prosthetic components, outcomes including functional efficacy, patient comfort, and longevity of the prosthesis may not always be highly predictable, especially if procedures are performed by physicians and surgeons with different levels of skill, experience, and frequency of repeating an individual procedure. This may be confirmed by various reports in the literature that suggest a positive relationship between outcomes and the numbers of procedures performed annually by individual surgeons.
Accurately determining and aligning an implant orientation is a difficult process requiring expensive equipment. A simple, efficient method is needed to reduce medical costs and time of the surgical procedure, while maintaining accuracy.